Corrosion inhibited lubricating oil



Chemi a m ny. t- L ia a: g norafiai- Delaware N D wi App i a i Apr SerialNo. 284,642

6 C ai (C1. 25243- This invention relates -to-new-lubrieating-oil compositions haying a high degree of oxidation stability. More;

particularly the present invention relates to, mineral llibiifeating oil compositions which have a materially decreased rate of corrosion in internal combustion engines, i. e. the gasoline and diesel engine and the like. This new improved lubricating oil comprises a mixture of a major amount of a hydrocarbon mineral lubricating oil and a minor amount of a member of the novel class of (tertalkylmercapto)-zinc N,N-dialkyl dithiocarbamates or mixtures thereof.

The use of an improperly formulated lubricating oil can cause severe damage in the engine with which it is employed requiring extensive motor overhaul. This damage is primarily related to the corrosion of the bearing surfaces of the motor and can be attributed to a number of factors. Even high grade, carefully refined hydrocarbon lubricating oils are subject to oxidation and break down in the modern engine, wherein the conditions of agitation, high temperature and pressure, the presence of the fuel combustion products which get by the piston rings into the oil and metallic catalysts present in the system all contribute to altering the properties of the lubricating oil. The fuel combustion produtes which enter the lubricant are termed blow-by gases and generally contain metallic catalysts derived from the decomposition of antiknock agents, etc. The alteration of the lubricating oil can also be accelerated by the bearing metal itself serving as a catalyst which metal surface is constantly reactivated by wiping. To meet this problem many oils contain additives which are generally called antioxidants or oxidation and bearing corrosion inhibitors.

Whereas the addition of efiicient antioxidants are desirable in all lubricating oils they are particularly necessary in oils employed in engines containing bearing metals which are susceptible to corrosion, as for example, highlead babbitts, cadmium alloys, copper-lead alloys, overplated copper alloys, and the like, which types of bearing metals are employed in a large percentage of the engines currently in use.

It has now been found that the novel compounds having the illustrative formula:

wherein R represents a tert-alkyl radical containing from 8 to 16 carbon atoms and R' and R" represent alkyl radicals containing up to 8 carbon atoms, have excellent properties as antioxidants in mineral lubricating oil compositions. The branched-chain alkyl radicals are specifically preferred for their oil-solubility characteristics.

The following (tert-alkylmercapto)-zinc N,N-dialkyl dithiocarbamates are illustrative of the novel antioxidants of this invention:

(Tert dodecylmercapto) zinc N,N dibutyl dithiocarbamate,

(Tert-octylrnercapto)-zinc N,N-dibutyl dithiocarbomate,

(Tert dodecylmercapto) zinc N,N-dimethyl dithiocarbamate,

(Tert hexadecylmercapto) zinc N,N dioctyl dithiocarbamate,

(Tert-octylmercapto)-zinc N,N-dimethyl dithioearbamate,

(Tert deeylmercapto) zinc N,N diisopropyl dithiocarbamate,

United Stflt$ Pate ice ('Ijert:tetradecylmercapto)=- zinc N;N"- dihexyl dithiocar bamate,,

(Tertdodecylmercapto), zinc N,N- diethyl dithiocare bamate,-H g (Terteoctylmercapto)'-zinc N,N-'dipentyl' dithioearbamate; (Tert-octylmercapto) zinc N,N di(2-ethylhexyl)' d'ithio' cat-bamate,. (Tert-hexadecylinercapto)izine N,N dimethyl dithioca'rbamate,. (Tert -he'xadecy lmercapto.) zinc N,N-dibutyl dithiocar t y (Tert-dodecylmercapto) zine N-ethyl N-heptyl dithiocarbamate, (Tert octylmerc'apto) zinc N-ethyl-N-methyl dithiocarbamate, and the likes The exact means .by which inhibitors decrease the potentially deleterious effectsof a lubricating oil in an engine are. not'k'nown'. It has been suggested'thatinhibitors mayfunc tion by decomposing the organic peroxides -as formed" to prevent a dangerous concentration-built up'of such defined to subject the formulation to conditions generally more severe that would be encountered in normal engine use. One such evaluation is known as the CRC Designation L454S (CRC Handbook, 1946 Edition: Coordinating Research Council, Inc., pages 394-418) or the L-4 engine test, which test was designed to determine the oxidation and bearing-corrosion characteristics of lubricating oils and was employed to evaluate the formulations of the present invention.

The following example is illustrative of this invention.

Lubricating oil compositions were prepared by mixing 0.5 and 1.0 parts by weight of (tert-dodecylmercapto)-zinc N,N-dibutyl dithiocarbamate with parts by weight of a solvent refined Mid-Continent SAE 30 oil until a homogeneous solution was obtained. The above oil formulations were then evaluated with the standard L-4 engine test with the following results:

Bearing Piston Total Percent Antioxidant Varnish Rating logeiirglgg.

It should be noted that tests were not completed using the straight mineral oil. Bearing weight losses of about 3000 mg. or more are meaningless for direct comparison with substantially lower values since practically all of the lead would be removed from the bearing and the corrosion rate would drop ofi rapidly. Thus the formulated oil compositions are substantially greater improvements than is indicated by the numerical data shown above.

The (tert-alkylrnercapto)-zinc N,N-dialkyl dithiocarbamate antioxidants are employed in amounts of from about 0.1 to about 5 or more parts by weight and preferably from about 0.5 to about 2 parts by weight per 100 parts by weight of the lubricating oil.

Other conventional motor oil additives can be used with the improved lubricating oil composition, as for example, other antioxidants, pour point depressants, viscosity index improvers, detergents, antifoam agents, rusting inhibitors, dyes and the like.

The novel antioxidants disclosed herein and the process of producing them are described and claimed in my copending application, Serial No. 284,641, filed April 26, 1952. The (tert-alkylmercapto)-zinc N,N-dialkyl dithiocarbamate antioxidants are prepared by the reaction of (A) substantially equimolecular quantities of (1) a dialkyl amine, (2) carbon disulfide, and (3) an alkali metal hydroxide in an aqueous medium; then adding thereto with agitation (B) a substantially equimolecular quantity of a zinc salt, wherein one anion is a water-solubilizing anion derived from a weak acid and the other anion is the tert- Ratented Dec. 7, 1954 alkylmercapto radical, dissolved in an inert water-immiscible solvent and continuing agitation for a sufficient time to effect substantially complete reaction. Then the solvent phase and the aqueous phase are allowed to separate and the aqueous phase removed and discarded. Thereafter the solvent phase is washed with water until substantially neutral and free from water-soluble salts. Then the solvent may be removed by distillation to recover the (tert-alkylmercapto)-zinc N,N-dialkyl dithiocarbamate.

I claim:

1. A lubricating oil composition comprising a major amount of a mineral lubricating oil and from about 0.1 to about 5 parts by weight per 100 parts by weight of the mineral lubricating oil of a (tert-alkylmercapto)-zinc LN-dlialky1 dithiocarbamate antioxidant having the ormu a:

wherein R represents a tcrt-alkyl radical containing from 8 to 16 carbon atoms and R and R" represent alkyl radicals containing up to 8 carbon atoms.

2. The lubricating oil composition of claim 1 wherein the antioxidant is (tert-dodecylmercapto)-zinc N,N-dibutyl dithiocarbamate.

3. The lubricating oil composition of claim 1 wherein the antioxidant is (tert-octylmercapto)-zinc N,N-dipentyl dithiocarbamate.

4. The lubricating oil composition of claim 1 wherein the antioxidant is (tert-hexadecylmercapto)-zinc N,N-dimethyl dithiocarbamate.

5. The lubricating oil composition of claim 1 wherein the antioxidant is (tert hexadecylmercapto)-zinc N,N-dibutyl dithiocarbamate.

6. The lubricating oil composition of claim 1 wherein the antioxidant is (tert-dodecylmercapto)-zinc N,N-diethyl dithiocarbamate.

References Cited in the file of this patent UNITED STATES PATENTS Name 

1. A LUBRICATING OIL COMPOSITION COMPRISING A MAJOR AMOUNT OF A MINERAL LUBRICATING OIL AND FROM ABOUT 0.1 TO ABOUT 5 PARTS BY WEIGHT PER 100 PARTS BY WEIGHT OF THE MINERAL LUBRICATING OIL OF A (TERT-ALKYLMERCAPTOE-ZINC N,N-DIALKYL DITHIOCARBAMATE ANTIOXIDANT HAVING THE FORMULA: 